Ear Embryology Flashcards
When and where do eyes first become evident in the developint embryo?
as optic (lens) placodes on the sides of the head around 4.5 weeks
When is the most critical period for eye development?
4-8 weeks (but really development continues after birth
What embryonic layers contribute to the eye?
neuroectoderm and surface ectoderm
What part of the developing brian does the eye stem off of?
diencephalon
What is the first step in eye development?
Before the rostral neuropore closes, you get formatin of optic grooves (eary in week 4)
What will the optic groove do?
It will evaginate outward so that the neural epithelium pushes outward through the mesenchyme towards surface ectoderm
This forms the optic vesicle.
What structure connects the optic vesicle to the rest of the idencephalon?
the optic stalk
During week 5, the optic vessicle folds back on itself to form what?
the optic cup
What are the layers of the optuc cup?
It’s a double walled structure with an outer and inner layer separated by the itnraretinal space
the inner layer will become neural retinal and the outer layer will become RPE
What induces the formation of the lens placode?
the optic cup
What does the lens placode do?
It invaginates and pinches off to sink down below the surface ectoderm. This is the lens vesicle and will eventually become the definiitive lens
During development, what artery supplies the lens vessicle?
the hyaloid artery
The creases of the optic cup approximate and fuse, tucking a fold of the neural tissue into the optic stalk. What is the inward creese called?
the choroid fissure (or optic fissure)
What usually happens to the hyaloid artery?
It persists until around 11 weeks, at which point it starts regressing - usually complete by about 8 months, but sometimes can persist into adulthood
THe hyaline artery becomes enclosed in the choroid fissure when the ends fuse together. What will this artery become then?
the central artery of the retina (the central vein joins it too, but i”m lazy)
What happens with a congenital coloboma?
you have defective closure of the choroid fisure, resulting in a key-hole deformity of the pupil.
An anterir coloboma is most common, but what symptoms will occur with a posterior coloboma?
the retina can be involved and there won’t be any neural ectoderm in the area where it didn’t fuse
this means you’‘ll have a huge blindsport
What does the retina form from>
the two layers of the optic cup
What induces the formation of the neural retina, choroid, and sclera?
the RPE
What is the ora serrata?
the junction between the multilayered photosensitive and simple non-photosensitive region of the retina
What will cuase re-establishment of the intraretinal space?
a detached retina - usually as a result of trauma
In what layer of the iris do the sphincter and dilator pupillae muscles develop? Why are they special developmentally?
They develop in the neuroectoderm layers of the iris
it’s an exception to the general rule that muscles develop from mesoderm
What is the pupillary membrane? What does its surround?
It’s remnants of mesenhyme on the anterior surface of the lens - usually disappears, but sometimes pieces can persista nd cause vision problems
What does the mesenchyme between the lens and the retina differentiate into?
vitreous body wiht virteous humor
What forms the choroid and sclera?
they’re layers that form from the surrounding mesenchyme, induced by the RPE
What layer is the equivalent of the arachnoid and pia around the optic nerve? Which is equivalent with the dura?
arachnoid and pia = choroid
dura = sclera
What induces the surface ectoderm to form the epithelium of the cornea and conjunctiva?
the lens
What are the 3 layers of the cornea?
epithelium (from surface ectoderm)
stroma (from mesenchyme)
endothelium (from neural crest cells)
At what week in development do the eyelids fuse? When do they reopen?
fuse around 10 weeks
open around 26 weeks
What is the classic triad of rubella associated congenital defects?
congenital cataracts
deafness
cardiac effects
What muscle needs to be tightened to fix congenital ptosis?
levator palpebrae
What is anopththalmia and microphthalmia and what is the treatment?
anophthalmia - no eye
microphthalmia - small eye
you put spacers into the orbit to gradually widen, and then use prosthetics
